Support sync mojo IPCs to and from bindings running on a sequence.

mojo/public/cpp/bindings/sync_handle_registry.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_SYNC_HANDLE_REGISTRY_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_SYNC_HANDLE_REGISTRY_H_
 
 #include <unordered_map>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
-#include "base/threading/thread_checker.h"
+#include "base/sequence_checker.h"
 #include "mojo/public/cpp/bindings/bindings_export.h"
 #include "mojo/public/cpp/system/core.h"
 
 namespace mojo {
 
-// SyncHandleRegistry is a thread-local storage to register handles that want to
-// be watched together.
+// SyncHandleRegistry is a sequence-local storage to register handles that want
+// to be watched together.
 //
 // This class is not thread safe.
 class MOJO_CPP_BINDINGS_EXPORT SyncHandleRegistry
-    : public base::RefCounted<SyncHandleRegistry> {
+    : public base::RefCountedThreadSafe<SyncHandleRegistry> {
  public:
-  // Returns a thread-local object.
+  // Returns a sequence-local object.
   static scoped_refptr<SyncHandleRegistry> current();
 
   using HandleCallback = base::Callback<void(MojoResult)>;
   bool RegisterHandle(const Handle& handle,
                       MojoHandleSignals handle_signals,
                       const HandleCallback& callback);
 
   void UnregisterHandle(const Handle& handle);
 
   // Waits on all the registered handles and runs callbacks synchronously for
   // those ready handles.
   // The method:
   //   - returns true when any element of |should_stop| is set to true;
   //   - returns false when any error occurs.
   bool WatchAllHandles(const bool* should_stop[], size_t count);
 
  private:
-  friend class base::RefCounted<SyncHandleRegistry>;
+  friend class base::RefCountedThreadSafe<SyncHandleRegistry>;
 
   struct HandleHasher {
     size_t operator()(const Handle& handle) const {
       return std::hash<uint32_t>()(static_cast<uint32_t>(handle.value()));
     }
   };
   using HandleMap = std::unordered_map<Handle, HandleCallback, HandleHasher>;
 
   SyncHandleRegistry();
   ~SyncHandleRegistry();
 
   HandleMap handles_;
 
   ScopedHandle wait_set_handle_;
 
-  base::ThreadChecker thread_checker_;
+  base::SequenceChecker sequence_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncHandleRegistry);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_SYNC_HANDLE_REGISTRY_H_